[gdal-dev] extracting a raster data within a polygon?

[Ahmet Temiz]

Awesome, thanks!

On Thu, Nov 14, 2019 at 9:39 AM Martin Chapman <mchapman at hyperacktive.com>
wrote:

> Ahmet,
>
>
>
> You can use either the gdalwarp.exe or the underlying gdal warper C++ API
> to create a new image using the polygon geometry as a cutline.  See the
> gdalwarp.exe or gdal warper C++ API documentation on how to do that.
>
>
>
> Basically, the cutline geometry will NULL out any pixels in the output
> image that are not within the polygon geometry.  If you use the
> gdalwarp.exe utility it will output a new image to disk.  If you use the
> gdal warper C++ API then you can write the output image to disk or memory.
> For more information on how this is done programmatically see the source
> code for the gdalwarp.exe that is included with the gdal source code.
>
>
>
> NOTE:  Your cutline geometry needs to be topologically correct in order to
> produce good output.  Topologically correct geometries do not contain
> self-intersections, slivers, etc.  An example of a self-intersecting
> geometry is a bow-tie where two lines in the geometry cross each other.
> Slivers are where two adjacent geometries share an edge but there is a gap
> between the edges.  Lots of shape files contain geometries that are not
> topologically correct because ArcMap and other tools don’t enforce that.
> The warp API can handle polygons and multi-polygons.  If your output comes
> out looking screwed up it is most likely because your cutline geometry is
> not topologically correct OR you didn’t convert the cutline geometry from
> coordinate space to pixel space before feeding it to the warper C++ API (in
> the case you do it programmatically).  The gdalwarp.exe can handle
> geometries in coordinate space.  If by chance your cutline geometry is not
> topologically correct you may be able to fix it by doing a Buffer()
> operation on it using the OGR API with a buffer distance of 0.  GEOS (the
> underlying engine for the OGR buffer operation) will create a new geometry
> that is exactly the same as the input because the buffer distance is zero
> but the GEOS API will attempt to correct the topology of the new geometry.
>
>
>
> Best regards,
>
> Martin Chapman
>
>
>
>
>
>
>
> *From:* gdal-dev [mailto:gdal-dev-bounces at lists.osgeo.org] *On Behalf Of *Ahmet
> Temiz
> *Sent:* Saturday, November 9, 2019 9:57 AM
> *To:* gdal-dev
> *Subject:* [gdal-dev] extracting a raster data within a polygon?
>
>
>
> Hi,
>
> how I can extract a raster data within a polygon (not a rectangle) using
> C++?
>
> i.e. dem within provincial boundary
>
> Regards
>
> --
>
> Ahmet Temiz
> Jeoloji Müh.
> Afet ve Acil Durum Yönetimi Başkanlığı
> Bilgi İşlem  Dairesi Başkanlığı-CBS Grubu
>
>
> ________________________
>
> Ahmet Temiz
> Geological Eng.
> Information Systems - GIS Group
> Disaster and Emergency Management
> of Presidency
>


-- 
Ahmet Temiz
Jeoloji Müh.
Afet ve Acil Durum Yönetimi Başkanlığı
Bilgi İşlem  Dairesi Başkanlığı-CBS Grubu


________________________

Ahmet Temiz
Geological Eng.
Information Systems - GIS Group
Disaster and Emergency Management
of Presidency
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